The first version of the MG Midget was essentially a badge engineered version of the Austin-Healey Sprite MKII and retained the quarter elliptic sprung rear axle from the original Sprite. The engine was a 948 cc A-Series with twin SU carburettors producing 46 hp (34 kW) at 5,500 rpm and 53 lbfÂ·ft (72 Nm) at 3,000 rpm. Brakes were drum all round. In 1963 the engine was increased to 1,098 cc raising the output to 56 hp (42 kW) at 5,500 rpm and 62 lbfÂ·ft (84 Nm) at 3,250 rpm and disc brakes replaced the drums at the front. The doors had no external handles or locks and the windows were sliding Perspex side screens. A heater was an optional extra.

Externally the main changes were to the doors, which gained wind up windows, quarter lights and external handles, and the windscreen which got a new frame. The hood (US - top) though modified, continued to have a removable frame that had to be erected before the cover was put on. The rear springs were replaced by more conventional half elliptical types. The engine got better bearings allowing the power to be increased to 59 hp (44 kW) at 5,750 rpm and torque to 65 lbfÂ·ft (88 Nm) at 3500 rpm. 26,601 were made.

For the MkIII MG Midget (1966-1974) the engine now grew to 1,275 cc using the development seen on the Mini Cooper S. Output was 65 hp (48 kW) at 6,000 rpm and 72 lbfÂ·ft (98 Nm) at 3,000 rpm. However, this was a de-tuned version of the engine that was given to the Cooper S. The Midget retained the standard 12G940 cylinder head casting that was common to other BMC 1300 cars, whereas the Cooper S had a special head with an extra two bolts to fasten it to the cylinder block. The hood was now permanently attached to the car. There were minor changes to the body in 1969 with the sills painted black and a revised black grille. "Rostyle" wheels were standardised but wire spoked ones remained an option. The square shaped rear wheel arches became rounded in January 1972. Also in this year, a Triumph steering rack was fitted, giving a gearing that was somewhat lower than earlier Midgets. A second exhaust silencer was also added in 1972.

In order to meet US federal regulations, large black plastic bumpers (usually called rubber bumpers, despite not actually being rubber) were added in 1974, to the front and rear and the ride height was increased. The A-Series engine was dropped to be replaced by the 1,493 cc unit from the Triumph Spitfire and a modified Morris Marina gearbox with synchromesh on all four gears. The round rear wheel arches were now square again to increase the body strength.

The last car was made on December 7th 1979 after 73,899 of the last version had been made. There was no Austin-Healey Sprite equivalent. However there was a limited number of cars produced in 1980 of the MG Midget.